September 14, 2000
12:00 AM (EDT)

News Release Number: STScI-2000-31

Centaur's Bright Surface Spot Could be Crater of Fresh Ice

September 14, 2000: The unexpectedly varied surface of a wayward piece of space debris has given astronomers new insights into the
characteristics and behavior of a ghostly population of faintly observed comet-like bodies that lie just beyond Pluto's orbit.
While observing an object called 8405 Asbolus, a 48-mile-wide (80-kilometer-wide) chunk of ice and dust that lies
between Saturn and Uranus, astronomers using the Hubble telescope were surprised to find that one side of the object
looks like it has a fresh crater less than 10 million years old, exposing underlying ice that is apparently unlike any yet seen.
This shows that these mysterious objects, called Centaurs, do not have a simple homogenous surface. Hubble didn't
directly see the crater - the object is too small and far away - but a measure of its surface composition with its
near-infrared camera shows a complex chemistry.

Q & A: Understanding the Discovery

1.
What is the composition of the ice?

The researchers aren't certain about the ice's makeup. Their analysis suggests that some sections of the ice possess strong similarities to water ice. The astronomers speculate that the chunk of ice could be composed of a new combination of known ingredients.

2.
Have astronomers observed other Centaurs?

By latest count, scientists have discovered 21 Centaurs. These small, dim, icy bodies are considered escapees from a vast reservoir of comets, the Kuiper Belt beyond Pluto. The Centaurs' orbits were disrupted, and the objects were flung into the region between the orbits of Neptune and Jupiter. The researchers speculate that the violent collision that caused the impact crater on 8405 Asbolus knocked it out of the Kuiper belt.